The invention relates to a method of evaluating electromagnetic radiation which is utilized for representing at least one parameter of an area or region which is to be monitored. It also relates to a device for evaluating electromagnetic radiation utilized for representing at least one parameter of an area or region which is to be monitored, the device having a measuring head which is opreatively connected to a receiver and a transmitter, wherein the measuring head forms a boundary surface for the area or region to be monitored.
Electromagnetic radiation is evaluated in all areas of technology in the most varied functional connections. However, in this context reference is only made by way of example to control technology, e.g. in the form of light barriers, measurement and analysis technology, e.g. in the form of optically spectroscopic methods and not least safety and monitoring technology, e.g. for monitoring multiple-phase flows to avoid operational malfunctions as a consequence of obstructions, but also as a consequence of flying sparks or a developing seat of a fire. Particularly in relation to applications which are intended to provide warnings about dangerous operational states, there is a greater need to monitor the systems installed for this purpose to ensure that they function in problem-free manner. To this end, various technologies techniques are also already known.
Light barriers typically consist on the one hand of a transmitting unit and on the other hand a receiving unit lying opposite thereto at a spaced interval, wherein the receiving unit is arranged for receiving an electromagnetic signal transmitted by the transmitting unit and wherein the interruption in reception in turn serves to trigger a signal, a switching procedure or the like. As an alternative, these light barriers are also known in the form, wherein a light signal which is continuously emitted by a transmitting unit is reflected on a mirror unit, wherein in turn a receiving unit is provided which receives the reflected signal. It is known to treat the problem of increasing attenuation which is associated with increasing contamination of the surface intended for coupling the signal in and out, by virtue of the fact that a reduction in the received signal level below a specified value is interpreted as the beginning of an operational malfunction, and furthermore before there is a complete failure of the light barrier. In this case, there is no function-monitoring of the evaluation circuits within the transmitting and receiving unit used, so that malfunctions, e.g. cable fracture or the like are not readily identifiable in this area.
Electromagnetic radiation is utilized in a very broad spectral range and moreover is always tailored to suit the specific application, wherein insignificant spectral portions of radiation are generally blanked out. From the Applicant's brochure “Überwachungsanlage für MDF-Zyklon ABC 7” [monitoring system for MDF-cyclone ABC 7], it is known in the case of a cyclone separator used for the purpose of switching off the solids, in particular fibrous substances, to monitor the formation of a material build-up in the outlet region by installing a transmitting unit and a receiving unit which lie diametrically opposite one another in the walls of the separator and which are arranged to transmit and receive infrared radiation respectively, wherein the signal level is able to indicate the instantaneous solids charge of the flow within the separator and where an obstruction is beginning to form the pneumatic conveyance can be automatically switched off.
Another brochure by the Applicant entitled “Funkenlöschanlagen Sicherheit für Ihre Produktion” [spark extinguishment systems; safety for your production] discloses so-called spark detectors which can used for monitoring flying sparks in pneumatic conveyance systems. The spectral sensitivity of these detectors is tailored to the recognition of sparks or other dangerous elements which are inflammable, e.g. smolder spots, and are each formed by receiving units which are disposed in such a manner as to lie diametrically opposite each other in relation to the pipe line which is to be monitored. In order to test the smooth operation of the evaluation circuits, a test diode is also provided which emits a test signal which is identified and interpreted by the receiving unit. This function test which can be performed manually or in an automated manner according to e.g. specifiable time intervals or can even be performed automatically in an event-controlled manner renders it possible reliably to examine the spark detector for any internal malfunctions or damage, i.e. within the evaluation circuits. In the case of spark detectors of this type, it is also known to provide an external test probe in the pipe line in order to check for any possible contamination of the areas intended for coupling in the radiation which is to be received, said test probe lying opposite e.g. the spark detector to be examined and serving to generate a test signal, the reception quality of which renders it possible to derive information relating to the level of contamination. However, on the one hand this necessitates the provision of an aperture for assembly of the test probe and is thus characterized by an increased installation outlay. In addition, there is the problem that in general the test probe will also be subjected to the same conditions of contamination as the spark detector itself which is to be examined, so that in spite of the increased outlay, it is not reliably possible to rule out malfunctions as a result of contamination.
Finally, German patent publication DE 195 31 917 C1 discloses a detector for electromagnetic radiation which is designed as a flame detector for the purpose of monitoring areas or industrial processes, wherein both a receiver and also a transmitter are disposed within a housing with a window which is intended for coupling-in radiation to be received, wherein radiation emanating from the transmitter is reflected on the inner side of the window surface and wherein the contamination of the outer side of the window can be detected with the aid of the reflection characteristics thereof, so that the monitoring procedure is performed by the evaluation of the reflected signal. Although this device is able to establish that the outer side of the window has been contaminated, the evaluation circuits or the device are not examined as well.
The mode of operation of a device which is used to monitor a pipe line for pneumatic conveyance can be impaired by an accumulation of material within the pipe line, by contamination of the surface intended for coupling-in the radiation and by defects in electrical evaluation circuits. Using these known devices it is not possible to counteract these possible sources of disruption completely.
Against this background, it is the object of the invention to provide a method of the type mentioned in the introduction where possible without any additional installation outlay such that possible external and internal sources of disruption, which impair the working result, can be identified in a problem-free manner and in particular can be localized. In the case of a method of the generic type, this object is achieved by using a second measuring head disposed opposite to a first measuring head.
Accordingly, it is essential to the invention that the area to be monitored is allocated at least two measuring heads in a mutually opposite-lying arrangement, each one of said measuring heads being arranged for the purpose of coupling radiation in and out. The measuring heads can thus be configured completely identical to each other. With respect to their spectral sensitivity, they are preferably arranged in such a manner that the radiation received is merely that which corresponds to the parameter of the area to be monitored. By way of example only and without limitation, it is possible to mention the procedure of monitoring the area for the occurrence of heat sources, e.g. sparks, so that a considerable safety risk can depend upon the smooth execution of the method. It is then essential to the invention that function-testing is performed with the proviso that the transmitter of one measuring chain emits a defined test signal, e.g. a test pulse which is reflected in part on the boundary surface for the area to be monitored, wherein this part is received by the receiver of the same measuring chain. A further part of the test signal passes through the boundary surface and crosses the area, which is to be monitored, up to the receiver of the opposite-lying measuring chain. Signals which describe the two said radiation portions are thus provided at the outputs of the two measuring chains, wherein on the basis of these two signal portions it is possible, e.g. by a comparison with reference signals to derive a statement relating to the current mode of function of the device. The reflected signal portion can be used for example to identify the level of contamination of the boundary surface, as its reflection behavior is changed in a characteristic manner precisely by this contamination. By means of the signal which passes through the boundary surface and is received by the receiver of the opposite-lying measuring head it is possible to identify and examine the state of the area as such in the same manner as the function of the measuring chain. If the device is used, for example, in the case of a pipe line used for the pneumatic transportation of solids, it is possible using the last-named signal portion to derive a statement relating to an unusual accumulation of material inside the pipe line. Conversely, in addition to providing indicators to the contamination of the boundary surface, it is also possible using the first signal portion to produce a statement relating to the function of the electronic devices which are intended for the evaluation of the received signal portion and for the generation of an electrical measurement value describing said signal portion. Therefore, as a departure from the prior art, it is not only possible in accordance with the invention to detect external contamination of a boundary surface but also at the same time to incorporate into this test the current state of the area including the opposite-lying measuring head. A test procedure of this type which is initiated by triggering a test pulse via the measuring head is consequently triggered in an identical manner via the transmitter of the second measuring head, so that at the end of one complete testing cycle, a statement is provided relating to the current state of the two measuring heads. As a further departure from the prior art set forth in the introduction, the omission of one particular test probe means that there is a reduced engagement into the walls of the area to be monitored and thus reduced installation outlay overall, as existing lines of the measuring heads are utilized for the transmission of control signals, e.g. for triggering a test pulse and for acknowledging received signals.
It is also the object of the invention to provide a device which is designed to perform the method and which in comparison with the prior art is characterized by a lower installation outlay and a greater degree of reliability in the detection of operational malfunctions of the device which are in the stages of development. In the case of this type of device, this object is achieved by each measuring chain including a measuring head, a transmitter and a receiver arranged to receive radiation emitted by the transmitter of an oppositely positioned measuring chain.
The essential components of the device consist of at least two measuring chains and a control and evaluation unit which is disposed at a regular spaced interval from said measuring chains. For their part, the measuring chains consist of a measuring head, which forms the boundary surface for the area to be monitored, a transmitter and a receiver and evaluation circuits which are disposed downstream thereof and which are intended and arranged on the one hand to generate a test signal and to emit it via the transmitter and on the other hand to receive radiation via the receiver and to convert it into an electrical measurement signal which describes this radiation. Each measuring chain is thus arranged on its end lying opposite the measuring head for bi-directional communication with the control and evaluation unit. The latter is intended to trigger the test procedure as such and in particular to subject the provided measuring chains consecutively to the inventive checking procedure set forth in the introduction, and to compare the respectively received electrical signals, which characterize a predetermined progression of a received test signal, with reference signals, wherein this comparison is used to derive a statement relating to the current state of the device. Furthermore, with the aid of the different radiation portions, which are received in each case as the system response, namely on the one hand the reflected radiation portion and on the other hand the radiation portion which has passed through the area up to the receiver of the opposite-lying measuring head, it is possible to derive differentiated statements relating to the type of possible malfunction.
In dependence upon the directional characteristic of the functional elements used for coupling the radiation in and out, the number of measuring chains connected within the framework of a device in accordance with the invention is governed by virtue of the fact that the area to be monitored is covered completely. If permitted by the directional characteristics, two measuring chains can be sufficient.
In the most convenient case, a transmitter and a receiver are located in each case in a closed housing which is separated from the area, which is to be monitored, by virtue of a window which acts in a sealing manner. However, it is also possible to form the boundary surface for the area, which is to be monitored, directly by the end side of an optical wave guide. The temperatures of the atmosphere prevailing within the area which is to be monitored determine whether the area contains mechanically or chemically aggressive substances.
In an advantageous manner, the optical wave guide is utilized bi-directionally, so that it is possible to couple radiation in and out over the same boundary surface for the area which is to be monitored. At the end remote from the area which is to be monitored, the optical wave guide end cooperates with a transmitter and a receiver which in this case are always disposed in pairs. This embodiment of the device has the particular advantage that the said boundary surface can be disposed at a spaced interval with respect to the functional elements, in which the coupled-in radiation is evaluated, so that the last-named location is not subjected to the possibly unfavourable thermal influences of the area which is to be monitored.
There are many ways of forming the measuring chain, in particular its functional elements which are utilized for the purpose of forming and evaluating the measurement value.
In accordance with one emboidment, it is provided that disposed between the window of the measuring head on the one hand and a receiver/transmitter pair is an element of an optical wave guide which thus forms part of the signal transmission path.
In accordance with another embodiment, it is provided that all of the elements of a measuring chain can be disposed within a single housing which thus forms a constructional unit which is arranged to receive a signal, which triggers a testing procedure, or is arranged for the transmission of an electrical signal which describes a received radiation portion. The comparison with a reference signal can be performed in the measuring head itself and only the result can be relayed to a control and evaluation unit. In the latter case, the control and evaluation unit assumes only the synchronization of the transmission and reception processes. The spatial distribution of the elements of a measuring chain can thus be selected according to considerations of expediency. In particular, the control and evaluation unit can also be integrated into the measuring chain and disposed together with this in a common housing.
A further embodiment is directed to variations in the practical formation of the connection between a control and evaluation unit on the one hand and the measuring chains on the other hand. Generally, the control and evaluation unit is disposed some distance apart from the measuring chains which is particularly advantageous in the case of relatively large installations. The connection can be formed by cable but also by optical wave guides, in particular flexible optical wave guides—however, it is also possible to consider a radio path.
It is particularly expedient if the control and evaluation unit is provided with an external interface which is intended to establish a connection with a higher-ranking control system. For example, this can be the control system of the installation which incorporates the area which is to be monitored, since it is also possible in this manner to assist in achieving a meaningful test result. Therefore, it is possible to tailor the test procedure to suit the process being performed in the installation, so that, for example, test procedures are not performed if there is already a substantial material loading in the said area, in order to prevent a corresponding contamination from being signaled in error as a result of substantial attenuation of the received signal.